AdelaideTandem

Hi All,

We have a Cannondale RT3000 (2002 model I think) with Edco competition hubs and Mavic T519 rims.

We just got back from a Bicycle South Australia tour on which we broke 4 drive side spokes in 4 days doing about 370km (230mi). We had broken 2 spokes in the previous 4 years. They are DT spokes but I am not sure which type.

We have only gone 3700km on the bike in 4 years as we only use it for tours. Combined weight of my wife and I is about 125kg (275lbs) and the most we ever put on it is a day pack of about 10kg (22lbs)

I guess it is time for a wheel rebuild as the tension must be off on some of the spokes and was wondering if anyone could recommend which spokes we should use as replacements.

A guy on the ride who works at Abbotsford cycles in Melbourne recommended DT Alpine III spokes as what they use whenever they get a serial spoke breaker.

Any suggestions?

Cheers

A

TandemGeek

Three:

- Don't use the triple-butted Alpine III's; the heads are VERY fat and often times get overly distressed at the spoke hole during the initial wheel build. A lot of folks -- myself included -- thought the Alpine III's would be a tandem wheel builder's dream; however, that was not the case as already described.

- Do use double-butted spokes.

- Do make sure your wheel builder knows how to build a very high-tension wheel that is checked with a tensionometer before and after distressing the wheel.

waterrockets 

+1

I'd add that it may be worth considering thinner double-butted non-drive spokes as they will be less likely to go slack even though they have less tension than the drive side. The reason is that they have to elongate more than a thicker spoke to provide the tension, so the displacement required to make them slacken is greater than for a thicker spoke.

TandemGeek

FWIW, most tandems with 145mm - 160mm rear spacing use symetrically-laced rear wheels, which is to say that they have equal static tension on left and right side rear spokes.

The exception may be on certain disc equiped tandems that re-use single MTB disc hub bodies vs tandem-specific hubs that maintain the non-dished rear wheel design, even at the expense of steeper bracing angles.

waterrockets 

Right, I guess that's especially true considering they're built to accomodate the drum brakes, as that pushes the nondrive flange toward the center of the axle.

So any guesses as to why the OP is busting drive-side spokes?

TandemGeek

Because the wheel either wasn't built with equal tension around the spoke network or the rim was previously damaged after hitting a pothole or road obstacle and, as a result, the spoke that flexed the most happened to be on the drive side and broke first. When it broke, the rest of the drive side spokes were weakened. Given that it sounds like the initial spoke fix was a field repair, the replacement spoke was likely installed and then tightened the required amount to put the rear wheel back in true and I doubt the rest of the spokes were checked for proper tension. Thus, the now weakened and non-equally tensioned spokes quickly began to fail in short order which is what I'd expect to see.

Rule of thumb: One spoke breaks, no big deal. Second spoke breaks shortly there after rebuild the wheel. Given their touring scenario, the latter was not necessarily an option. Moreover, if the spoke breakage occurs after a really hard "hit", suspect rim damage as well.

AdelaideTandem

Thanks for all the advice, it is very helpful, particularly the Alpine III opinions.

The fix for the first (and later second) spoke breakage was done at the bike shop where we bought it but they are a big place with lots of staff and I have no idea who would have repaired it.

Although neither were a field repair it is likely that TandemGeek is correct and the rest of the spokes weren't checked for tension (I didn't even know to ask but I will now). I will also use TG's 2 spoke rule of thumb.

I had a good look at the rim and there aren't any visible signs of cracks or dents. Are there any other signs that I should be looking for?

As far as spokes go, does anyone have any opinions on the other DT spokes like the competition or the champion? The reason I am so fixated on the DT spokes currently is just due to availability.

Now if I can just find a good wheel builder in Adelaide....

Thanks

A

TandemGeek

The rim ding was mentioned only as another possible cause of the loss of spoke tension other than initial build tension issues or low-tension wheels which are more often the cause of spoke fatigue.

As for the spokes, you'd want to use the double-butted DT Competition or SuperComp, not the straight gauge Champion.

waterrockets 

You can quickly check tension by plucking spokes. If they all play the same note, then they are the same tension. The drive side will probably not be the same tension as the non-drive, although given TandemGeek's input earlier, they are likely to be really close. Still, I'd just compare drive side spokes and non-drive spokes independant of each other. Front wheel should sound the same for all the spokes, both sides.

If you get the tensions regular, and the rim turns out to be true, your wheel might have some real life left in it. Make sure the wheel is stress-relieved with a lot of force. That will likey expose any fatigued spokes by snapping them at the bend (wear gloves and safety glasses if you're doing it yourself).

To be conservative, the wheel probably does need a rebuild though. Being frugal like I am, I'd keep the current wheel alive as long as it remains reasonably dependable (which may be long past )

Competition, since they are double butted. Champions are straight guage: https://www.dtswiss.com/index.asp?fus...ikedetail&id=7

It actually makes a stronger wheel to have a thinner middle section for your spokes since they elongate more to reach tension, so they lose less tension when the rim displaces. You don't want them so thin that they wind up during wheel maintenance.